The invention relates to a surgical implant for use in a method for widening a vertebral canal of a vertebra of the spine, in particular in laminoplasty and laminectomy methods.
The vertebral canals of the vertebrae of the spine form what is known as the spinal canal, in which the spinal cord, covered by the spinal meninges, is contained.
The spinal cord as part of the central nervous system may be impaired in its functions if pressure is exerted on the spinal cord, as occurs for example in spinal canal stenosis, a condition which can be attributable to a number of causes, such as the presence of spondylosis or ossification of the posterior longitudinal ligament.
This situation may be remedied by enlarging the vertebral canal of the vertebra or vertebrae of the spine that is or are affected so that the spinal cord has more space available to it and can therefore evade the pressure.
An overview of the therapy options commonly used to date can be found for example in F. Meyer et al., Deutsches Ärzteblatt, Volume 105, Issue 20, pages 366 to 372. Aside from the ventral methods, various dorsal methods are used, namely laminectomy with and without fusion and laminoplasty. Optionally, ventral methods may also be used in combination with dorsal methods.
Among the various dorsal methods, laminoplasty necessitates the least intervention in the bone substance.
Various surgical techniques for performing laminoplasty have been proposed heretofore, and of these the two most important are described and referred to in literature as the single door technique or the double door technique. An overview of these techniques and an assessment of the effects to be expected in terms of pressure relief and widening of the spinal canal may be found for example in the publication by Wang, Xiang-Yang et al. in SPINE, Vol. 31, No. 24, 2006, pages 2863 to 2870.
In what is known as the single door technique, also known as the open door technique, the lamina is cut through on one side of the vertebra, forming an incision gap, while a groove is created on the other side of the lamina, without the vertebral arch being cut through.
In the subsequent opening up of the vertebral canal, the region of the vertebral arch that has the groove acts as a kind of hinge and allows the vertebral arch to be opened, this being accompanied by fracture of the bone substance. The vertebral arch remains joined to the vertebral body by the periosteum and the collagenous fibres of the bone substance.
What is known as the double door technique involves cutting through or completely removing the spinous process of a vertebra and placing a groove in the lamina on each of the two sides of the spinous process; here again, the regions of the vertebral arch containing the grooves act as hinges. The vertebral, canal is now opened up by swinging apart the two vertebral arch sections with the associated spinous process portions, if still existing, and as before the bone substance in the area of the hinges breaks. Here, too, the vertebral arch sections remain connected to the vertebral body by the periosteum and the collagenous fibres of the bone substance.
Using either technique, the vertebral canal of the vertebrae is fixed in the opened up state by way of implants. Aside from autologous bone graft, a hydroxyapatite spacer or the like is used as an implant material.
Despite the reduced degree of intervention in the bone substance as compared with other dorsal methods, a significantly increased rate of subsequent neck pain is still regarded as a disadvantage of laminoplasty, as is a restriction in motion of the cervical spine which is often observed.
It is an object of the invention to propose an implant which enables widening of the vertebral canal of vertebrae with less stress on the patient.